Pregnancy is a process that require structural and functional changes in maternal body, including the urinary system. Alterations in the bladder capacity and function during pregnancy are related to the occurrence of gestational Urinary Incontinence (UI). Experimental studies also have evidenced functional changes in the bladder, such as decreased contractility and increased bladder compliance in pregnant rats. However, studies that aim to evaluate pregnancy-induced morphological changes in the bladder are scarce. Thus, the aim of this preclinical study was to analyze the impact of pregnancy on the morphology of the bladder in rats.

This preclinical study was approved by the Institutional Animal Care and Use (protocol number 007/2016). At 90 days of age, Wistar female rats were mated overnight with one male rat for the maximum period of 15 days. The vaginal smear was performed every morning to confirm the presence of spermatozoa, which characterized gestational day 0. After mating, the animals were distributed in Pregnant (P) (n=10) and Virgin (V) groups. On gestational day 21, the rats were euthanized with Thiopentax (120 mg/kg) and urinary bladder samples were obtained, and studied by Masson's Trichrome staining for collagen fiber analysis. Simultaneously, dissection of the urinary bladder and preparation of histological slides of the virgin rats' bladders were performed. The histological slides were analysed in a light microscope (Olympus Corporation® / BX41TF) and morphological and morphometric analysis of total collagen area (100 sections/group, magnification 10x) were performed using CellSens Standard software (Olympus Corporation®). Data are expressed as mean ± standard deviation (SD). Comparisons of measurements among groups were performed by Student-t test. For all statistical comparisons, p<0.05 was considered statistically significant.

The morphological analysis of both groups (GP and GV) showed usual histological structure of the bladder, including urothelium, lamina propria, smooth muscle, blood vessels and collagen fibers. The morphometric analysis showed increased total collagen area in P group compared with V group (p<0,0001).

Bladder functions depends on the balance between neural transmission, detrusor contractility and elastic elements, including collagen that participate on the structural bladder support. Thus, alterations in the collagen deposition may be related with pathological conditions. There is evidence that deficiency of collagen production is related with the occurrence of Stress Urinary Incontinence (SUI) during pregnancy due to the insufficient support of urogenital tract. In contrast, increased collagen deposition was detected in the detrusor and in the lamina propria of bladder with decreased compliance, which evidences that there might be a correlation between alterations in the bladder collagen area and bladder dysfunction during pregnancy.

Pregnancy increased the collagen deposition in the bladder of female rats. Further studies are necessary to confirm the correlation between changes in the bladder collagen area and possible bladder dysfunction during the gestational period.

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